The present invention relates to an isolating switch for metal-clad, compressed-gas insulated high-voltage switchgears having an isolating distance between electrodes and able to be short-circuited by a tubular, movable main contact pin, whose fixed mating contact has a hollow design. The movable main contact pin may contain an auxiliary contact pin, which is capable of moving axially in the main contact pin and which with its end facing the isolating distance, penetrates a clamping ring inside the main contact pin and is surrounded by a spring, which extends between the clamping ring and a limit stop on the auxiliary contact pin. In the neutral position, the auxiliary contact pin is situated inside the movable main contact pin and, in the closed position of the isolating switch, abuts on a spring-loaded mating contact situated in the hollow mating contact of the main contact pin. At the beginning of the opening movement of the movable main contact pin, it remains in this manner until it is returned to the neutral position with a velocity that is greater than the movement of the movable main contact pin by the spring after being released by a mechanical control unit permanently mounted inside one of the field plates.
This type of isolating switch is disclosed by EP O 066 533 B1. In the known isolating switch, both the auxiliary contact pin as well as its mating contact are each surrounded by a spring. This spring biases the auxiliary contact pin and the mating contact in the opening direction. To secure the contact in the closed position, a latching mechanism connects the auxiliary contact pin and its mating contact in an interlocking manner, which is why one of the two parts must execute an angular movement. When the isolating switch is switched off, the triggering of this angular movement and thus the release of the auxiliary contact pin is effected by a mechanical control unit at a predetermined instant based on the position of the main contact pin, namely when the main contact pin has reached the dielectric distance to the field plate of the mating contact necessary to guarantee a dielectric strength. After that, the auxiliary contact pin is retracted by its spring with a velocity greater than that of the main contact pin. Therefore, with the known isolating switch, electric arcs of low amperages can also be extinguished without damage occurring, for example, when off-load transformers are switched off.
The triggering of the opening movement of the auxiliary contact pin can, in fact, be set exactly in the known isolating switch, but the latching action of these known devices is not free of friction. Therefore, materials of the parts coming into contact with one another during the latching action require certain properties. Nevertheless, one cannot, with certainty, prevent wear of the parts and, therefore the triggering instant is adversely affected.
Therefore, the present invention overcomes these problems of known switches by simplifying the construction of an isolating switch of this type and designing the triggering of the auxiliary contact pin so that it is largely free of friction and not subject to wear.